When it comes down to which team was more evil, well I can't really choose either of them. Some of the members in each team were evil but take the whole teams as groups and they weren't. When it comes to Magma, their ideals involved wanting purely land and no water but stopped realizing it would destroy the planet, not to mention everything and everyone would die without water. As for Plasma, most of the team was misguided into believing they were fighting to free Pokemon from bad trainers or to just free Pokemon in general, until it was noted later that Ghetsis really didn't care and just wanted to rule the world. So now, there's still followers of Ghestsis, knowing his ideals and wanting the same thing, so I guess the current Plasma is considered evil. Though I do like Magma more than Plasma for one important reason: they're less annoying and repetitive.